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Setting Gravity for Convection

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Old   June 21, 2010, 07:27
Default Setting Gravity for Convection
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James Lamb
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I am modelling the passive cooling of a heat sink in an enclosure. I have created a volume of air with a stagnation inlet below and a pressure outlet above. When setting gravity in this model it creates a large flow downwards. I expected to see buoyancy forces at work on the hot components, this does not seem to be the case. Am I not leaving the simulation long enough or could I need more inner iterations? At the moment I am running for a minute with 2 inner iterations per second.

Thanks for the help in advance.

James
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Old   June 21, 2010, 10:00
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Vinicius Girardi
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Are you using the coupled solver?
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Old   June 21, 2010, 10:05
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Not at the moment no.
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Old   June 21, 2010, 10:11
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Vinicius Girardi
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Try to use the coupled solver and use more inner iterations, maybe you also can check your time-step, you should have a compromise between your time-step size and your number of inner iterations...
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Old   June 21, 2010, 10:13
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Ok just re-meshing now with a coupled solver. Thank you for your help
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Old   June 22, 2010, 02:30
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Look at your courant number.
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Old   June 25, 2010, 11:49
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To see the gravity effects, your reference density should be really really close to the density of the fluid at that temperature. Make sure the difference between reference density and density less than 1e-7.
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Old   June 25, 2010, 13:20
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Jipp or some steady tests before to check the density "effect" - with and withput gravity.
Or what do you think?
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Old   June 25, 2010, 14:27
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After initializing the solution, write a filed function to calculate the difference between the density in a cell ($Density) and the reference density value. Create a scene with this field function to see the density difference. Then try to readjust the reference density value (and also the value in field function) to make the difference as small as possible.
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